Discharging circuit for a piezoelectric device

ABSTRACT

In a piezoelectric actuator, a first driving signal amplified a predetermined sine wave is applied to a piezoelectric device in a direction parallel to a polarization direction thereof. A second driving signal having a negative phase with respect to the first driving signal which is amplified the sine wave is applied to the piezoelectric device in a direction opposite to the polarization direction. Thus, the piezoelectric device is driven by a driving signal amplified the first or second driving signal double. Voltages of the first and second driving signals are much smaller than a voltage of inversion of polarization of ceramic thin plates constituting the piezoelectric device.

This application is a divisional of U.S. patent application Ser. No.09/456,184, filed Dec. 7, 1999, now U.S. Pat. No. 6,703,762 B1, theentire contents of which are hereby incorporated by reference. Thisapplication is also based on patent application Hei. 10-359568 filed inJapan, the contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an actuator and a driving apparatus of theactuator, and especially relates to a truss type actuator or an impacttype actuator for moving a driven object by utilizing a displacementgenerated in a piezoelectric device when an alternating driving voltageis applied thereto.

2. Description of the Related Art

A piezoelectric device shows piezoelectric effect for expanding orcontracting a displacement substantially in proportion to a level of avoltage when the voltage is applied in a direction parallel to thepolarization direction thereof. Thus, a piezoelectric device isconventionally proposed to be used as an actuator for supplying adriving force to a driven object. The piezoelectric device used in thepiezoelectric actuator is polarized in unidirectional. Electrodes areprovided on both end faces of the piezoelectric device in thepolarization direction thereof and output terminals of a driving circuitare connected thereto, so that driving signal from the driving circuitcan be applied between the electrodes.

In an impact type piezoelectric actuator, a friction member, whichcontacts a driven object, is provided to contact an end face of thepiezoelectric device in a direction parallel to the direction of thedisplacement (expansion or contraction) of the piezoelectric device. Animpact voltage signal rapidly rising up is applied to the piezoelectricdevice for quickly expanding (or contracting) the piezoelectric device,so that one of the friction member and the driven object is relativelymoved in a direction. Subsequently, another voltage signal slowlyfalling down is applied to the piezoelectric device for slowlycontracting (or expanding) the piezoelectric device, so that thefriction member and the driven object are moved in the oppositedirection at the same time. Thus, the driven object is moved in apredetermined direction.

In a truss type piezoelectric actuator, two rod-shaped piezoelectricdevices are provided for crossing at a predetermined angle, for example,at right angle and a driving member contacting a driven object isprovided at a cross point of the piezoelectric devices. Two alternatingdriving voltages having a phase difference between them are respectivelyapplied to the piezoelectric devices for moving the driving member alongan elliptic trail. Thus, the driven object, which is intermittentlymoved with the driving member, is rotated or linearly moved in apredetermined direction (see, for example, U.S. Pat. No. 4,613,782).

In such the piezoelectric actuator, the displacement (quantity of theexpansion and the contraction) can be increased by increasing the levelof the voltage applied to the piezoelectric devices. However, when thepiezoelectric actuator is used, for example, in a handy type equipmentsuch as a camera, it is difficult to generate a high voltage drivingsignals for driving the piezoelectric devices, since electric energy ofa battery is consumed by electric devices such as a motor for winding afilm or for adjusting a position of a taking lens, an electro-magnet forcontrolling shutter speed or for controlling a size of an aperturediaphragm, and so on. Furthermore, a DC/DC converter, a smoothingcapacitor, and so on are newly necessary or become larger than theconventional ones for increasing the voltage of the driving signals ofthe piezoelectric devices. Thus, a configuration of a driving signalgenerating circuit becomes more complex and larger than the conventionalone, so that it is difficult to downsize the equipment using thepiezoelectric actuator and to reduce the cost of the driving circuit orthe equipment.

For information, in the art of audio equipment, it is conventionallyknown that an input signal of one of two amplifiers is inverted andoutput terminals of both of two amplifiers are respectively connected tocoils of speakers (Bridge Tied Load connection) for increasing outputpower of the speakers. However, such the conventional method merelyinverts the audio signal and the object to be applied is theelectro-magnet which has no relation with respect to the polarization.Thus, it is impossible to apply the conventional method to thepiezoelectric device for increasing the output power thereof, since itis necessary to regard the polarization in the piezoelectric device.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an actuator and adriving apparatus thereof, in which voltage of the driving signals ofthe actuator is maintained in a low level with regard to inversion ofthe polarization, but the displacement of the actuator can be increaseddouble. Furthermore, the apparatus using the actuator and the drivingapparatus can be downsized and be inexpensive.

An actuator driven by a driving apparatus comprises a piezoelectricdevice serving as a driving source when a driving signal is applied in apolarization direction thereof. A driving apparatus in accordance withan aspect of the present invention comprises: a waveform generator forgenerating a signal varying corresponding to the passage of time; afirst driver for generating a first voltage signal having a maximumvoltage smaller than a voltage of inversion of polarization of thepiezoelectric device by using the signal from the waveform generator,and for applying the first voltage signal to the piezoelectric device inthe polarization direction; and a second driver for generating a secondvoltage signal having a maximum voltage smaller than the voltage ofinversion of polarization of the piezoelectric device and the samepolarity as that of the first driving signal by using the signal fromthe waveform generator, and for applying the second voltage signal tothe piezoelectric device in a direction opposite to the polarizationdirection.

By such a configuration, the piezoelectric device is substantiallydriven by a driving signal amplified double of the conventional drivingsignal, so that the displacement of the piezoelectric device becomessubstantially double in comparison with the conventional one. However,the voltage of the driving signal can be much smaller than the voltageof the inversion of polarization of the piezoelectric material. Thepresent invention can be applied to both of a truss type actuator and animpact type actuator.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view showing a configuration of a truss typepiezoelectric actuator in a first embodiment of the present invention;

FIG. 2 is a block diagram of a driving apparatus in the first embodimentsuitable for driving the truss type piezoelectric actuator;

FIG. 3 is a circuit diagram of the driving apparatus shown in FIG. 2;

FIGS. 4A to 4D are drawings showing waveforms of voltages at points A toD in the circuit shown in FIG. 3;

FIG. 5 is a circuit diagram of a driving apparatus in a secondembodiment of the present invention;

FIGS. 6A to 6D are drawings showing waveforms of voltages at points A toD in the circuit shown in FIG. 5;

FIG. 7 is a graph showing characteristic curves showing relationsbetween the voltage of the driving signals and the displacements of theactuator in the embodiments of the present invention;

FIG. 8 is a perspective view showing a configuration of an impact typepiezoelectric actuator in a third embodiment of the present invention;

FIG. 9 is a cross-sectional front view showing a configuration of a partof the actuator shown in FIG. 8;

FIG. 10 is a perspective view showing a configuration of a modificationof the impact type piezoelectric actuator in the third embodiment;

FIG. 11 is a side view of the actuator shown in FIG. 10;

FIG. 12 is a block diagram of a driving apparatus in the thirdembodiment suitable for driving the impact type piezoelectric actuator;

FIG. 13 is a circuit diagram of the driving apparatus shown in FIG. 12;

FIGS. 14A to 14D are drawings showing waveforms of voltages at points Ato D in the circuit shown in FIG. 13;

FIG. 15 is a circuit diagram showing a configuration of a drivingapparatus in a fourth embodiment of the present invention;

FIGS. 16A to 16D are drawings showing waveforms of voltages at points Ato D in the circuit shown in FIG. 15;

FIG. 17 is a block diagram showing a configuration of a drivingapparatus in a fifth embodiment of the present invention;

FIGS. 18A to 18D are circuit diagrams respectively showing configurationof inside portions in a driving circuit in FIG. 17;

FIG. 19 is a timing chart showing a driving signal and timings of on andoff of terminals in a control circuit in FIG. 17;

FIGS. 20A to 20D are circuit diagrams respectively showing configurationof inside portions in a driving circuit in a driving apparatus in asixth embodiment of the present invention;

FIG. 21 is a timing chart showing a driving signal and timings of on andoff of terminals in a control circuit in FIG. 20;

FIG. 22 is a circuit diagram showing a configuration of a drivingapparatus in a seventh embodiment of the present invention;

FIG. 23 is a timing chart showing a driving signal and timings of on andoff of terminals in a control circuit in FIG. 22;

FIG. 24 is a circuit diagram showing a configuration of a drivingapparatus in an eighth embodiment of the present invention;

FIG. 25 is a timing chart showing a driving signal and timings of on andoff of terminals in a control circuit in FIG. 24;

FIG. 26 is a circuit diagram showing a configuration of a drivingapparatus in a ninth embodiment of the present invention; and.

FIG. 27 is a circuit diagram showing a configuration of a drivingapparatus in a tenth embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENT

First Embodiment

An actuator and a driving apparatus thereof in a first embodiment of thepresent invention is described with reference to FIGS. 1, 2, 3 and 4A to4C.

A configuration of a truss type piezoelectric actuator in the firstembodiment is shown in FIG. 1. A base member 10 is fixed on a frame of astationary apparatus (not shown in the figure). The base member 10 hastwo contacting faces 101 and 102 which will cross at right angle if theyare extended. A first piezoelectric device 11 and a second piezoelectricdevice 12 respectively have substantially the same rectangularparallelepiped shape and the same configuration. Base ends of the firstand second piezoelectric devices 11 and 12 are fixed on the contactingfaces 101 and 102. Thus, the first and second piezoelectric devices 11and 12 cross substantially at right angle. A driving member 13 isprovided at crossing point of the first and second piezoelectric devices11 and 12, and fixed on top ends of the first and second piezoelectricdevices 11 and 12. As can be seen from FIG. 1, the driving member 13 hasa fan shaped cross-section having an interior angle about 90 degrees andhaving a predetermined thickness perpendicular to a paper sheet ofFIG. 1. An outer cylindrical surface 131 of the driving member 13 havinga predetermined friction coefficient by a surface treatment is disposedfor facing outside. A driven object 100 contacts the cylindrical surface131 of the driving member 13 with a predetermined pressure, so that iscan be moved in a direction shown by arrow X by a elliptical movement ofthe driving member 13.

The first and second piezoelectric devices 11 and 12 are configured bypiling up of a plurality of ceramic thin plates such as PZT (Pb, Zr, Ti)showing piezoelectric characteristic and two (first and second) groupsof electrodes, alternately. The ceramic thin plates and the electrodesare fixed by adhesive. The first and second groups of the electrodes arerespectively connected to a positive and a negative terminals of adriving electric power source via cables.

When a predetermined voltage is applied between the first and secondgroups of the electrodes, electric fields are generated in respectiveceramic thin plates disposed between an electrode in the first group andan electrode in the second group in a direction parallel to the pilingup of the ceramic thin plates and the electrodes. The directions of theelectric fields are alternately the same direction. The ceramic thinplates are piled in a manner so that the polarization of them arealternately the same direction. In other words, the polarizationdirection of the adjoining two ceramic thin plates are opposite to eachother. Thus, all the ceramic thin plates can be displaced in the samedirection even when the same driving signal is applied to the first andsecond groups of the electrodes.

A block diagram of a driving apparatus in the first embodiment which issuitable for the truss type piezoelectric actuator is shown in FIG. 2. Afirst driving circuit 16 is connected to the first piezoelectric device11, and a second driving circuit 17 is connected to the secondpiezoelectric device 12. The first driving circuit 16 comprises awaveform generator 161, a first driver 162, an inverter 163 and a seconddriver 164. An output terminal of the first driver 162 is connected to aterminal of the first piezoelectric devices 11, and an output terminalof the second driver 164 is connected to the other terminal of the firstpiezoelectric device 11.

Similarly, the second driving circuit 17 comprises a waveform generator171, a first driver 172, an inverter 173 and a second driver 174. Anoutput terminal of the first driver 172 is connected to a terminal ofthe second piezoelectric devices 12, and an output terminal of thesecond driver 174 is connected to the other terminal of the secondpiezoelectric device 12. Phases of driving signals outputted from thewave for generator 161 and 171 are different, as described below.

A circuit diagram of the first driving circuit 16 is shown in FIG. 3.The second driving circuit 17 has substantially the same configuration,so that the illustration and the description of the second drivingcircuit 17 are omitted. The first driver 162 is configured by anoperational amplifier OP11, resistors R11 and R12, and a constantvoltage power supply B11. The inverter 163 and the second drivingcircuit 164 are integrally configured by an operational amplifier OP12,resistors R13 and R14, and a constant voltage power supply B12. In thefirst embodiment, the operational amplifiers OP11 and OP12 arerespectively connected to a conventional constant voltage power supplyfor supplying a voltage of 5V. The output voltage of the constantvoltage power supply B11 is set to be 0.5V, and that of the constantvoltage power supply B12 is set to be 1.83V.

A noninverting input terminal of the operational amplifier OP11 isconnected to an output terminal of the waveform generator 161, and aninverting input terminal thereof is connected to the constant voltagepower supply B11 via the resistor R12.

Furthermore, the resistor R11 is connected between an output terminaland the inverting input terminal of the operational amplifier OP11 forfeedback. The output terminal of the operational amplifier OP11 isconnected to one group of the electrodes of the first piezoelectricdevice 11. Thus, an amplification factor α of the operational amplifierOP11 becomes double corresponding to a relation α=(1+R11/R12), and thephase of the output signal from the operational amplifier OP11 becomesthe same as that of the input signal.

A noninverting input terminal of the operational amplifier OP12 isconnected to the constant voltage power supply B12, and an invertinginput terminal thereof is connected to the output terminal of thewaveform generator 161 via the resistor R14. Furthermore, the resistorR13 is connected between an output terminal and the inverting inputterminal of the operational amplifier B12 for feedback. The outputterminal of the operational amplifier OP12 is connected to the othergroup of the electrodes of the first piezoelectric device 11. Thus, anamplification factor β of the operational amplifier OP12 becomes doublecorresponding to a relation β=(−R13/R14), and the phase of the outputsignal from the operational amplifier OP12 is inverted. When the inputsignal is alternating such as a sine wave, the phase of the outputsignal from the operational amplifier OP12 becomes negative with respectto that from the operational amplifier OP11.

An operation of the driving apparatus in the first embodiment isdescribed with reference to FIGS. 4A to 4D. FIGS. 4A, 4B and 4Crespectively show waveforms of voltage signals at points A, B and C inFIG. 3. FIG. 4D shows a waveform of a driving signal (hereinafterabbreviated as driving signal D) applied to the piezoelectric device 11shown by arrow D in FIG. 3.

The waveform generator 161 generates a sine wave shown in FIG. 4A(hereinafter abbreviated as sine wave A), in which the voltage of thesine wave varied in a range between 0.5V and 2.5V for considering thestability of the operation of the circuit. The operational amplifierOP11 amplifies the sine wave A and outputs an amplified driving signalshown in FIG. 4B (hereinafter abbreviated as driving signal B) havingthe same phase as that of the sine wave A. The voltage of the drivingsignal B is varied in a range between 0.5V and 4.5V. The operationalamplifier OP12 amplifies the sine wave A and outputs an amplifieddriving signal shown in FIG. 4C (hereinafter abbreviated as drivingsignal C) having the negative phase with respect to that of the sinewave A. The voltage of the driving signal C is varied in a range between0.5V and 4.5V having the same polarity as that of the driving signal B.

The driving signal B from the operational amplifier OP11 is applied tothe (first) piezoelectric device 11 in the same direction as thepolarization direction of the ceramic thin plates constituting thepiezoelectric device 11. On the other hand, the driving signal C fromthe operational amplifier OP12 is applied to the piezoelectric device 11in a direction opposite to the polarization direction. When thepiezoelectric device 11 is expanded by the driving signal B from theoperational amplifier OP11, the driving signal C from the operationalamplifier OP12 is applied to the piezoelectric device 11 in a directionfor contracting it, and vice versa. Thus, it is substantially equivalentthat the driving signal D shown in FIG. 4D is applied to thepiezoelectric device 11. As mentioned above, two driving signals B and Chaving the same polarity and the same voltage variation of 4V (0.5V to4.5V) is respectively applied to the same piezoelectric device 11 inopposite directions, so that the maximum displacement of thepiezoelectric device 11 can be increased to the same level as that whenthe voltage variation of the driving signal B or C is amplified double(8V: −4V to +4V).

Characteristic curves showing relations between the voltages applied tothe piezoelectric device (abscissa) and the displacements of thepiezoelectric device (ordinates) are shown in FIG. 7. In thisembodiment, a known material showing the inversion of the polarizationat the voltage of −20V or +20V is used as the material of the ceramicthin plates. A predetermined voltage larger than 20V is applied to theceramic thin plates for polarizing the direction of axes of crystalscontained in the ceramic thin plates. The ceramic thin plates are piledin a manner so that the polarization of them are alternately the samedirection. Furthermore, the electrodes connected to positive andnegative terminals of the driving electric power source are alternatelypiled up.

As mentioned above, the level of the voltage applied to thepiezoelectric devices 11 and 12 is in a range between −4V and +4V in thepolarization direction, so that the level or absolute value of thevoltage of the driving signal of the piezoelectric device (−4V to +4V)is sufficiently smaller than that of the voltage of the inversion of thepolarization of the ceramic thin plates (−20V or +20V). Thus, there isno problem of the linearity of the relation between the displacement ofthe piezoelectric device and the voltage applied thereto.

In case that the polarization of the ceramic thin plates is treated atthe voltage of +20V, the larger the voltage applied to the piezoelectricdevices 11 and 12 increases from 0V to +4V, the larger the displacementor quantity of the expansion of the piezoelectric device increases fromthe standard point O of the displacement (along the line designated byC1 but in the opposite direction of the arrow). Alternatively, thesmaller the voltage applied to the piezoelectric devices 11 and 12decreases from 0V to −4V, the larger the displacement or quantity of thecontraction of the piezoelectric device increases from the standardpoint O of the displacement (along the line designated by C1 and in thesame direction of the arrow).

In case that the polarization of the ceramic thin plates is treated atthe voltage of −20V, the smaller the voltage applied to thepiezoelectric devices 11 and 12 decreases from 0V to −4V, the larger thedisplacement or quantity of the expansion of the piezoelectric deviceincreases from the standard point O of the displacement (along the linedesignated by C2 but in the opposite direction of the arrow).Alternatively, the larger the voltage applied to the piezoelectricdevices 11 and 12 increases from 0V to +4V, the larger the displacementor quantity of the contraction of the piezoelectric device increasesfrom the standard point O of the displacement (along the line designatedby C2 and in the same direction of the arrow).

The second driving circuit 17 generates a driving signal having apredetermined phase difference such as 90 degrees advanced or delayedwith respect to the driving signal D shown in FIG. 4D. Since the firstpiezoelectric device 11 and the second piezoelectric device 12 arerespectively driven by sine wave driving signals having the phasedifference of 90 degrees between them, the driving member 13 is movedfor trailing an ellipse (including a circle). As a result, the drivenobject 100 contacting the driving member 13 with the predeterminedpressure will be moved in the direction shown by arrow X in FIG. 1. Formoving the driven object 100 in the opposite direction, the phasedifference between the driving signal of the first piezoelectric device11 and that of the second piezoelectric device 12 is switched advancedelay. The phase difference between the driving signals is preferably 90degrees but not restricted by this value.

Second Embodiment

An actuator and a driving apparatus thereof in a second embodiment ofthe present invention is described with reference to FIGS. 5 and 6A to6C. A configuration of a truss type piezoelectric actuator and a blockdiagram of a driving apparatus in the second embodiment aresubstantially the same as those in the first embodiment, so that theillustration and the description of them are omitted.

A circuit diagram of a first driving circuit 26 of the driving apparatusin the second embodiment is shown in FIG. 5. A second driving circuit 27has substantially the same configuration as that of the first drivingcircuit 26, so that the illustration and the description of the seconddriving circuit 27 are omitted. A first driver 262 is configured by anoperational amplifier OP21, resistors R21 and R22, and a constantvoltage power supply B21. An inverter 263 and a second driving circuit264 are integrally configured by an operational amplifier OP22,resistors R23 and R24, and a constant voltage power supply B22. Inthe-second embodiment, the operational amplifiers OP21 and OP22 arerespectively connected to a conventional constant voltage power supplyfor supplying a voltage of 5V. The output voltage of the constantvoltage power supply B21 is set to be 1.83V, and that of the constantvoltage power supply B22 is set to be 1.3V.

A noninverting input terminal of the operational amplifier OP21 isconnected to an output terminal of the waveform generator 261, and aninverting input terminal thereof is connected to the constant voltagepower supply B21 via the resistor R22. Furthermore, the resistor R21 isconnected between an output terminal and the inverting input terminal ofthe operational amplifier OP21 for feedback. The output terminal of theoperational amplifier OP21 is connected to one group of the electrodesof the first piezoelectric device 21. Thus, an amplification factor γ ofthe operational amplifier OP21 becomes quadruple corresponding to arelation γ=(1+R21/R22), and the phase of the output signal from theoperational amplifier OP21 becomes the same as that of the input signal.

A noninverting input terminal of the operational amplifier OP22 isconnected to the constant voltage power supply B22, and an invertinginput terminal thereof is connected to the output terminal of thewaveform generator 261 via the resistor R24. Furthermore, the resistorR23 is connected between an output terminal and the inverting inputterminal of the operational amplifier B22 for feedback. The outputterminal of the operational amplifier OP22 is connected to the othergroup of the electrodes of the first piezoelectric device 21. Thus, anamplification factor Δ of the operational amplifier OP22 becomesquadruple corresponding to a relation Δ=(−R23/R24), and the phase of theoutput signal from the operational amplifier OP22 is inverted. When theinput signal is alternating, the phase of the output signal from theoperational amplifier OP22 becomes negative with respect to that fromthe operational amplifier OP21.

An operation of the driving apparatus in the second embodiment isdescribed with reference to FIGS. 6A to 6D. FIGS. 6A, 6B and 6Crespectively show waveforms of voltage signals at points A, B and C inFIG. 5. FIG. 6D shows a waveform of a driving signal (hereinafterabbreviated as driving signal D) applied to the piezoelectric device 21shown by arrow D in FIG. 5.

The waveform generator 261 generates a sine wave shown in FIG. 6A(hereinafter abbreviated as sine wave A), in which the voltage of thesine wave varied in a range between 0.5V and 2.5V for considering thestability of the operation of the circuit. The operational amplifierOP21 amplifies an input signal corresponding to the sine wave A andoutputs a half-wave rectified sine wave shown in FIG. 6B (hereinafterabbreviated as driving signal B) with the same phase as that of theinput signal, in which the voltage of the driving signal B is varied ina range between 0.5V and 4.5V. The operational amplifier OP22 amplifiesan input signal corresponding to the sine wave A and outputs a half-waverectified sine wave shown in FIG. 6C (hereinafter abbreviated as drivingsignal C) with the negative phase with respect to that of the inputsignal, in which the voltage of the driving signal C is varied in arange between 0.5V and 4.5V.

In the second embodiment, the amplification factors γ and Δ of theoperational amplifiers OP21 and OP22 are respectively set to bequadruple, and the phases of the driving signals B and C are negativewith each other. Furthermore, the voltages of the constant voltage powersupplies B21 and B22 are adjusted so as to apply only the positivevoltages in alternating driving signals (actually, larger than +0.5V forstabilizing the driving circuit). Thus, it is substantially equivalentthat the driving signal D shown in FIG. 6D, which is amplified double incomparison with the conventional driving signal, is applied to thepiezoelectric device 21.

Third Embodiment

An actuator and a driving apparatus thereof in a third embodiment of thepresent invention is described with reference to FIGS. 8, 9, 10. 11, 12,13 and 14A to 14C.

A configuration of an impact type piezoelectric actuator in the thirdembodiment is shown in FIGS. 8 and 9. In FIG. 8, a rod shaped stationarymember (first unit) 30 a is hollowed except both ends and a centerpartition 301 a for forming a first cavity 302 a and a second cavity 303a. A piezoelectric device 31 a is provided in the first cavity 302 a ina manner so that a direction of piling up of the ceramic thin platescoincides with an axis of the stationary member 30 a and the base end ofthe piezoelectric device 31 a is fixed on the stationary member 30 a. Asliding rod 32 a and a slider (second unit) 33 a which is engaged withouter cylindrical face of the sliding rod 32 a are provided in thesecond cavity 303 a. The sliding rod 32 a penetrates holes serving asbearings of the sliding rod 32 a and formed on the center partition 301a and the end face of second cavity 303 a of the stationary member 30 a.An end of the sliding rod 32 a contacts a top end of the piezoelectricdevice 31 a and the other end of the sliding rod 32 a penetrates andprotrudes a little from the stationary member 30 a. Thus, the slidingrod 32 a is movable in the axial direction thereof shown by arrow Y inFIG. 8.

As can be seen from FIG. 9, the slider 33 a comprises a base member 330a, a friction member 332 a and a plate spring 335 a. The base member 330a has two walls 331 a formed on both ends thereof in a directionparallel to the axis of the sliding rod 32 a. The friction member 332 ahas a protrusion 334 a contacting the plate spring 335 a and receiving apressure from the plate spring 335 a. A bearing hole 333 having acircular cross-section is formed on each wall 331 a through which thesliding rod 32 a penetrates. Circular concave faces having the sameradius are respectively formed on a portion of the friction member 332 aand on a portion of the base member 330 a between the walls 331 a forfacing each other. The sliding rod 32 a is nipped between the basemember 330 a and the friction member 332 a by a pressure of the platespring 335 a. Another plate spring 304 a is provided on the outer faceof the end of the second cavity 303 a of the stationary member 30 a forapplying a pressing force to the sliding rod 32 a toward thepiezoelectric device 31 a in the axial direction thereof (see FIG. 8).

By such a configuration, the sliding rod 32 a is held by the slider 33 awith a pressure suitable for impact sliding motion. When the sliding rod32 a is quickly moved in a first direction by the displacement of thepiezoelectric device 31 a, the slider 33 a can not move with the slidingrod 32 a due to inertia thereof. Thus, the slider 33 a relatively slideson the sliding rod 32 a. On the other hand, when the sliding rod 32 a isslowly moved in a second direction opposite to the first direction bythe displacement of the piezoelectric device 31 a, the slider 33 a canmove with the sliding rod 32 a by the friction force generated betweenthem. By repeating these motions, the slider 33 a is moved in the seconddirection. Detailed description of the movement of the actuator will bedescribed below.

A modified configuration of the impact type piezoelectric actuator inthe third embodiment is shown in FIGS. 10 and 11. FIG. 10 illustrates acondition that a driving unit (first unit) 30 b is detached from astationary unit (second unit) 34 b. The stationary unit 34 b isconfigured by a flat base member 341 b and two slender guide members 351b and 352 b. The guide members 351 b and 352 b are disposed on the basemember 341 b in parallel with each other with a predetermined gap. Theguide member 352 b has an angular or a circular concave groove on a sidefacing the other guide member 351 b for serving as a stopper of themoving unit in upper direction with respect to the base member 341 b.

The driving unit 30 b comprises a piezoelectric device 31 b, a frame 32b for holding the piezoelectric device 31 b and a slider 33 b. The frame32 b has a rod shape with a first space 322 b and a second space 332 bseparated by a partition 321 b. The piezoelectric device 31 b isprovided in the first space 322 b in a manner so that a direction ofpiling up of the ceramic thin plates coincides with the lengthwisedirection of the frame 32 b and the base end of the piezoelectric device31 b is fixed on the frame 32 b. A cylindrical shaped slider 33 b havinga shaft is provided in the second space 323 b. The outer diameter of thecylindrical shape of the slider 33 b substantially coincides with thewidest gap between the guide members 351 b and 352 b. The shaft of theslider 33 b penetrates holes servings as bearings of the shaft and areformed on the center partition 321 b and the end face of the secondspace 323 b of the frame 32 b. An end of the shaft of the slider 33 bcontacts a top end of the piezoelectric device 31 b with a predeterminedpressure by a pressing member such as a spring not shown in the figure.Thus, the slider 33 b is movable in the lengthwise direction of theframe 32 b shown by arrow Y in FIG. 10.

A block diagram of a driving apparatus in the third embodiment suitablefor the impact type piezoelectric actuator is shown in FIG. 12. Thepiezoelectric device 31 a or 31 b is connected to a driving apparatus36. The driving apparatus 36 comprises a waveform generator 361, a firstdriver 362, an inverter 363 and a second driver 364. An output terminalof the first driver 362 is connected to a terminal of the piezoelectricdevice 31 a or 31 b, and an output terminal of the second driver 364 isconnected to the other terminal of the piezoelectric device 31 a or 31b.

A circuit diagram of the driving apparatus 36 is shown in FIG. 13. Thefirst driver 362 is configured by an operational amplifier OP31,resistors R31 and R32, and a constant voltage power supply B31. Theinverter 363 and the second driving circuit 364 are integrallyconfigured by an operational amplifier OP32, resistors R33 and R34, anda constant voltage power supply B32. In the third embodiment, theoperational amplifiers OP31 and OP32 are respectively connected to aconventional constant voltage power supply for supplying a voltage of5V. The output voltage of the constant voltage power supply B31 is setto be 0.5V, and that of the constant voltage power supply B32 is set tobe 1.83V, similarly to the first embodiment.

The waveform generator 361 generates a sawtooth wave (including atriangular wave and a trapezium wave) shown in FIG. 14A, in which theinclination in the rising up portion is different from that in thefalling down portion.

A noninverting input terminal of the operational amplifier OP31 isconnected to an output terminal of the waveform generator 361, and aninverting input terminal thereof is connected to the constant voltagepower supply B31 via the resistor R32. Furthermore, the resistor R31 isconnected between an output terminal and the inverting input terminal ofthe operational amplifier OP31 for feedback. The output terminal of theoperational amplifier OP11 is connected to one group of the electrodesof the first piezoelectric device 31 a or 31 b. Thus, an amplificationfactor ε of the operational amplifier OP31 becomes double correspondingto a relation ε=(1+R31/R32), and the phase of the output signal from theoperational amplifier OP31 becomes the same as that of the input signal.

A noninverting input terminal of the operational amplifier OP32 isconnected to the constant voltage power supply B32, and an invertinginput terminal thereof is connected to the output terminal of thewaveform generator 361 via the resistor R34. Furthermore, the resistorR33 is connected between an output terminal and the inverting inputterminal of the operational amplifier B32 for feedback. The outputterminal of the operational amplifier OP32 is connected to the othergroup of the electrodes of the first piezoelectric device 31 a or 31 b.Thus, an amplification factor ζ of the operational amplifier OP32becomes double corresponding to a relation ζ=(−R33/R34), and the phaseof the output signal from the operational amplifier OP32 is inverted.When the input signal is alternating, the phase of the output signalfrom the operational amplifier OP32 becomes negative with respect tothat from the operational amplifier OP31.

An operation of the driving apparatus in the third embodiment isdescribed with reference to FIGS. 14A to 14D. FIGS. 14A, 14B and 14Crespectively show waveforms of voltage signals at points A, B and C inFIG. 13. FIG. 14D shows a waveform of a driving signal (hereinafterabbreviated as driving signal D) applied to the piezoelectric device 31a or 31 b shown by arrow D in FIG. 13.

The waveform generator 361 generates a sawtooth wave shown in FIG. 14A(hereinafter abbreviated as sawtooth wave A), in which the voltage ofthe sine wave varied in a range between 0.5V and 2.5V. The operationalamplifier OP31 amplifies the sawtooth wave A and outputs a drivingsignal shown in FIG. 14B (hereinafter abbreviated as driving signal B)with the same phase as that of the sawtooth wave A. The voltage of thedriving signal B is varied in a range between 0.5V and 4.5V. Theoperational amplifier OP32 amplifies the sawtooth wave A and outputs anamplified driving signal shown in FIG. 14C (hereinafter abbreviated asdriving signal C) with the negative phase with respect to that of thesawtooth wave A. The voltage of the driving signal C is varied in arange between 0.5V and 4.5V with the same polarity as that of thedriving signal B. Thus, it is substantially equivalent that the drivingsignal D shown in FIG. 14D is applied to the piezoelectric device 31 aor 31 b. As mentioned above, two driving signals B and C having the samepolarity and the same voltage variation of 4V (0.5V to 4.5V) isrespectively applied to the same piezoelectric device 31 a or 31 b inopposite directions, so that the maximum displacement of thepiezoelectric device 31 a or 31 b can be increased to the same level asthat when the voltage variation of the driving signal B or C isamplified double (8V: −4V to +4V).

The movement of the impact type piezoelectric actuator shown in FIGS. 8and 9 is described. In a time period t1 to t2 in the driving signal Dshown in FIG. 14D, the voltage of the driving signal gradually increasesfrom −4V to +4V. The piezoelectric device 31 a slowly expands, and thesliding rod 32 a is slowly moved in a direction shown by arrow Y in FIG.8 against the pressure of the plate spring 304 a. At this time, sincethe moving speed of the sliding rod 32 a is slow, the slider 33 a ismoved with the sliding rod 32 a in the direction shown by arrow Y due tothe friction force generating between the contacting faces of thesliding rod 32 a and the slider 33 a. When the time reaches to t2, thevoltage of the driving signal D will be maintained at +4V until the timereaches to t3, so that the sliding rod 32 a and the slider 33 a arestopped at the position. When the time reaches to t3, the voltage of thedriving signal D rapidly decreases from +4V to −4V. Since thepiezoelectric device rapidly contracts corresponding to the falling downof the voltage, the sliding rod 32 a is quickly moved in the directionopposite to the direction shown by arrow Y. The slider 33 a, however,has been stopped at the position because the inertia of the slider 33 aovercomes the friction force between the sliding rod 32 a and the slider33 a. As a result, the slider 33 a is moved a predetermined distance inthe direction shown by arrow Y during one cycle of the driving signal D.By repeating the application of the driving signal D to thepiezoelectric device 31 a, the slider 33 a is intermittently moved inthe direction shown by arrow Y. For moving the slider 33 a in thedirection opposite to the direction shown by arrow Y, a sawtooth wavehaving the waveform of rapidly rising up and slowly falling down isgenerated by the waveform generator 361.

In the above-mentioned description, it is supposed that the slider 33 adoes not slide on the sliding rod 32 a when the movement of the sidingrod 32 a is slow. The slider 33 a, however, actually slides on thesliding rod 32 a even when the movement of the sliding member 32 a isslow corresponding to the intensity of the friction force between thesliding rod 32 a and the slider 33 a. In the latter case, the intensityof the force acting on the slider 33 a by the sliding rod 32 a isdifferent corresponding to the direction of the movement of the slidingrod 32 a, since the moving speed of the sliding rod 32 a is differentcorresponding to the direction of the movement. As a result, the slider33 a can be moved (see Publication Gazette of Unexamined Japanese PatentApplication Hei 7-298656).

Subsequently, the movement of the impact type piezoelectric actuatorshown in FIGS. 10 and 11 is described. In a time period t1 to t2 in thedriving signal D shown in FIG. 14D where the voltage of the drivingsignal gradually increases from −4V to +4V, the piezoelectric device 31b slowly expands, and the slider 33 b should be moved in a directionopposite to the direction shown by arrow Y in FIG. 10. At this time,since the speed of the expansion of the piezoelectric device 31 b isslow, the force acting on the contact faces of the slider 33 b and theguide members 351 b and 352 b is smaller than the static friction forcebetween them, so that the slider 33 b cannot be moved with respect tothe guide members 351 b and 352 b. As a result, the base member 32 b ofthe driving unit 30 b relatively moves in the direction shown by arrowY. When the time reaches to t2, the voltage of the driving signal D willbe maintained at +4V until the time reaches to t3, so that the basemember 32 b of the driving unit 30 b stops at the position. When thetime reaches to t3, the voltage of the driving signal D rapidlydecreases from +4V to −4V. Since the piezoelectric device rapidlycontracts corresponding to the falling down of the voltage, the slider33 b is quickly moved in the direction shown by arrow Y. At this time,the force acting on the contact faces of the slider 33 b and the guidemembers 351 b and 352 b is larger than the dynamic friction forcebetween them, so that the slider 33 a returns to an initial position onthe driving unit 30 b. As a result, the driving unit 30 b moves apredetermined distance in the direction shown by arrow Y during onecycle of the driving signal D. By repeating the application of thedriving signal D to the piezoelectric device 31 b, the driving unit 30 bintermittently moves in the direction shown by arrow Y. For moving thedriving unit 30 b in the direction opposite to the direction shown byarrow Y, a sawtooth wave having the waveform of rapidly rising up andslowly falling down is generated by the waveform generator 361.

Fourth Embodiment

An actuator and a driving apparatus thereof in a fourth embodiment ofthe present invention is described with reference to FIGS. 15 and 16A to16C. A configuration of an impact type piezoelectric actuator and ablock diagram of a driving apparatus in the fourth embodiment aresubstantially the same as those in the third embodiment, so that theillustration and the description of them are omitted.

A circuit diagram of a driving apparatus 46 in the fourth embodiment isshown in FIG. 15. A first driver 462 is configured by an operationalamplifier OP41, resistors R41 and R42, and a constant voltage powersupply B41. An inverter 463 and a second driving circuit 464 areintegrally configured by an operational amplifier OP42, resistors R43and R44, and a constant voltage power supply B42. In the fourthembodiment, the operational amplifiers OP41 and OP42 are respectivelyconnected to a conventional constant voltage power supply for supplyinga voltage of 5V. The output voltage of the constant voltage power supplyB41 is set to be 1.83V, and that of the constant voltage power supplyB42 is set to be 1.3V.

A noninverting input terminal of the operational amplifier OP41 isconnected to an output terminal of a waveform generator 461, and aninverting input terminal thereof is connected to the constant voltagepower supply B41 via the resistor R42. Furthermore, the resistor R41 isconnected between an output terminal and the inverting input terminal ofthe operational amplifier OP41 for feedback. The output terminal of theoperational amplifier OP41 is connected to one group of the electrodesof the first piezoelectric device 31 a or 31 b. Thus, an amplificationfactor η of the operational amplifier OP41 becomes quadruplecorresponding to a relation η=(1+R41/R42), and the phase of the outputsignal from the operational amplifier OP41 becomes the same as that ofthe input signal.

A noninverting input terminal of the operational amplifier OP42 isconnected to the constant voltage power supply B42, and an invertinginput terminal thereof is connected to the output terminal of thewaveform generator 461 via the resistor R44. Furthermore, the resistorR43 is connected between an output terminal and the inverting inputterminal of the operational amplifier B42 for feedback. The outputterminal of the operational amplifier OP42 is connected to the othergroup of the electrodes of the first piezoelectric device 31 a or 31 b.Thus, an amplification factor θ of the operational amplifier OP42becomes quadruple corresponding to a relation θ=(−R43/R44), and thephase of the output signal from the operational amplifier OP42 isinverted. When the input signal is alternating such as a sine wave, thephase of the output signal from the operational amplifier OP42 becomesnegative with respect to that from the operational amplifier OP41.

FIGS. 16A, 16B and 16C respectively show waveforms of voltage signals atpoints A, B and C in FIG. 15. FIG. 16D shows a waveform of a drivingsignal applied to the piezoelectric device 31 a or 31 b shown by arrow Din FIG. 15. An operation of the fourth embodiment by the driving signalD is substantially the same as that of the above-mentioned thirdembodiment, so that the description of the operation of the fourthembodiment is omitted.

Fifth Embodiment

A driving apparatus suitable in a fifth embodiment of the presentinvention is described with reference to FIGS. 17, 18A to 18D and 19.The driving apparatus in the fifth embodiment is suitable for drivingthe impact type piezoelectric actuators in the third embodiment shown inFIGS. 8 to 11.

A block diagram of the driving apparatus in the fifth embodiment isshown in FIG. 17. The driving apparatus 50 comprises a control circuit51, a driving circuit 52 and an electric power supply 53. A drivingsignal generated by the driving circuit 52 is applied to thepiezoelectric device 31 a or 31 b. The control circuit 51 outputsswitching signals I to VI shown in FIG. 19 corresponding to controlsignals to the driving circuit 52. The driving circuit 52 charges anddischarges the electric charge from the electric power supply into andfrom the piezoelectric device 31 a or 31 b corresponding to the controlsignals I to VI from the control circuit 51. When the piezoelectricdevice 31 a or 31 b is regarded as a capacitor, the voltages between theelectrodes of the piezoelectric device 31 a or 31 b is in proportion tothe quantity of the electric charge in the piezoelectric device 31 a or31 b. Thus, by changing the speeds for charging and discharging of theelectric charge into and from the piezoelectric device 31 a or 31 b, asawtooth wave driving signal shown in FIG. 19 can be applied to thepiezoelectric device 31 a or 31 b.

Circuit diagrams in the driving circuit 52 is shown in FIGS. 18A to 18D.As can be seen from FIG. 18A, four circuits are provided between theelectric power supply 53 and the ground, in which the circuits areconnected to the piezoelectric device 31 a or 31 b for configuring aseries circuit. Symbols P+ and P− added to the piezoelectric device 31 aor 31 b show the electrodes standardized by the polarization directionof the ceramic thin plate of the piezoelectric device.

A first circuit is configured by a constant current circuit 521 forsupplying a predetermined limited current to the piezoelectric device 31a or 31 b and a switching circuit 526. The first circuit serves as adischarge circuit for gradually discharging the electric charge from thepiezoelectric device 31 a or 31 b in a direction from the electrode P+to the electrode P−.

A second circuit is configured by switching circuits 522 and 526. Thesecond circuit serves as a quick charge circuit for quickly charging theelectric charge from the electric power supply 53 into the piezoelectricdevice 31 a or 31 b in a direction from the electrode P+ to theelectrode P−.

A third circuit is configured by switching circuits 523 and 525. Thethird circuit serves as a quick charge circuit for quickly charging theelectric charge from the electric power supply 53 into the piezoelectricdevice 31 a or 31 b in a direction from the electrode P− to theelectrode P+.

A fourth circuit is configured by a constant current circuit 524 forsupplying a predetermined limited current to the piezoelectric device 31a or 31 b and the switching circuit 525. The fourth circuit serves as adischarge circuit for gradually discharging the electric charge from thepiezoelectric device 31 a or 31 b in a direction from the electrode P−to the electrode P+.

A configuration of the constant current circuits 521 and 524 is shown inFIG. 18B. When level of the control signals I or IV is high, electriccurrent is shut off (switched off). Alternatively, when the level of thecontrol signals I or IV is low, the electric current is flown (switchedon).

A configuration of the switching circuits 522 and 523 is shown in FIG.18C. The switch circuits 522 and 523 are respectively configured by abipolar transistor. When level of the control signal II or III is high,electric current is shut off (switched off). Alternatively, when thelevel of the control signal II or III is low, the electric current isflown (switched on).

A configuration of the switching circuits 525 and 526 is shown in FIG.18D. The switch circuits 525 and 526 are respectively configured by abipolar transistor. When level of the control signal V or VI is low,electric current is shut off (switched off). Alternatively, when thelevel of the control signal V or VI is high, the electric current isflown (switched on).

In FIG. 19, the driving signal D shown a waveform standardized by thepolarization direction of the ceramic thin plate of the piezoelectricdevice. The control signals I to VI respectively correspond to timingsignals for switching on and off of the above-mentioned circuits 521 to526. The painted regions of the control signals I to VI by blackrespectively show the timings in which the control signals are switchedon for switching on the circuits 521 to 526.

An operation of the impact type piezoelectric actuator by the drivingapparatus in the fifth embodiment is described with reference to FIG.19.

For driving the impact type piezoelectric actuator in a first direction,the second circuit and the fourth circuit are alternately switched on.In a time period from t1 to t2, the control signals II and VI areswitched on, so that the switching circuits 522 and 526 constituting thesecond circuit are switched on. Thus, a predetermined short circuitedcurrent flows from the electric power supply 53 to the ground throughthe piezoelectric device 31 a or 31 b. The electric charge is charged inthe piezoelectric device 31 a or 31 b in a direction from the electrodeP+ to the electrode P− due to the capacitance thereof. Thus, the voltagebetween the electrodes P+ and P− rapidly increases to a level of thevoltage VP of the electric power supply 53. The level of the voltage VPis set to be lower than the level of the inversion of the polarizationof the ceramic thin plate of the piezoelectric device 31 a or 31 b. Inthis time period, the slider 33 a shown in FIGS. 8 and 9 is not movedwith respect to the stationary member 30 a. Similarly, the driving unit30 b shown in FIGS. 10 and 11 is not moved with respect to the basemember 34 b.

In a time period from t3 to t4, the control signals IV and V areswitched on, so that the constant current circuit 525 and the switchingcircuit 526 constituting the fourth circuit are switched on. In thefourth circuit, a predetermined constant current flows into thepiezoelectric device 31 a or 31 b in a direction from the electrode P−to the electrode P+, so that the electric charge charged at the time t2gradually is reduced. In other words, the electric charge charged in thepiezoelectric device 31 a or 31 b is gradually discharged. Thus, thevoltage between the electrodes P+ and P− gradually decreases to a levelof the voltage −VP. In this time period, the slider 33 a shown in FIGS.8 and 9 is moved in the first direction with respect to the stationarymember 30 a. Similarly, the driving unit 30 b shown in FIGS. 10 and 11is relatively moved in the first direction with respect to the basemember 34 b.

For driving the impact type piezoelectric actuator in a second directionopposite to the first direction, the rising up of the driving signal Dis gradually increased and the falling down thereof is rapidlyincreased. Concretely, output timings of the control signals from thecontrol circuit 51 is adjusted in a manner so that the control signalsIII and V are switched on in a time period from t11 to t12 for switchingon the third circuit, and the control signals I and VI are switched onin a time period from t13 to t14 for switching on the first circuit.

Sixth Embodiment

A driving apparatus in a sixth embodiment of the present invention isdescribed with reference to FIGS. 20A to 20D and 21. The drivingapparatus of the sixth embodiment is suitable for driving the impacttype piezoelectric actuators in the third embodiment shown in FIGS. 8 to11. The block diagram of the driving apparatus in the sixth embodimentis substantially the same as that in the fifth embodiment shown in FIG.17, so that the illustration thereof is omitted.

Circuit diagrams in the driving circuit are shown in FIGS. 20A to 20D.As can be seen from FIG. 20A, four circuits are provided between anelectric power supply 63 and the ground, in which the circuits areconnected to the piezoelectric device 31 a or 31 b for configuring aseries circuit. Symbols P+ and P− added to the piezoelectric device 31 aor 31 b show the electrodes standardized by the polarization of theceramic thin plate of the piezoelectric device.

A first circuit is configured by a switching circuit 621 and a constantcurrent circuit 626 for supplying a predetermined limited current to thepiezoelectric device 31 a or 31 b. The first circuit serves as adischarge circuit for gradually discharging the electric charge from thepiezoelectric device 31 a or 31 b in a direction from the electrode P+to the electrode P−.

A second circuit is configured by switching circuits 621 and 625. Thesecond circuit serves as a quick charge circuit for quickly charging theelectric charge from the electric power supply 63 to in a direction fromthe electrode P+ to the electrode P− of the piezoelectric device 31 a or31 b.

A third circuit is configured by switching circuits 622 and 624. Thethird circuit serves as a quick charge circuit for quickly charging theelectric charge from the electric power supply 63 to the piezoelectricdevice 31 a or 31 b in a direction from the electrode P− to theelectrode P+.

A fourth circuit is configured by a switching circuit 622 and a constantcurrent circuit 623 for supplying a predetermined limited current to thepiezoelectric device 31 a or 31 b. The fourth circuit serves as adischarge circuit for gradually discharging the electric charge from thepiezoelectric device 31 a or 31 b in a direction from the electrode P−to the electrode P+.

A configuration of the constant current circuits 623 and 626 is shown inFIG. 20B. When level of the control signals III or VI is low, electriccurrent is shut off (switched off). Alternatively, when the level of thecontrol signals III or VI is high, the electric current is flown(switched on).

A configuration of the switching circuits 621 and 622 is shown in FIG.20C. The switch circuits 621 and 622 are respectively configured by abipolar transistor. When level of the control signal I or II is high,electric current is shut off (switched off). Alternatively, when thelevel of the control signal I or II is low, the electric current isflown (switched on).

A configuration of the switching circuits 624 and 625 is shown in FIG.20D. The switch circuits 624 and 625 are respectively configured by abipolar transistor. When level of the control signal IV or V is low,electric current is shut off (switched off). Alternatively, when thelevel of the control signal IV or V is high, the electric current isflown (switched on).

In FIG. 21, the driving signal D shows a waveform standardized by thepolarization direction of the ceramic thin plate of the piezoelectricdevice. The control signals I to VI respectively correspond to timingsignals for switching on and off of the above-mentioned circuits 621 to626. The painted regions of the control signals I to VI by blackrespectively show the timings in which the control signals are switchedon for switching on the circuits 621 to 626.

An operation of the impact type piezoelectric actuator by the drivingapparatus in the sixth embodiment is described with reference to FIG.21.

For driving the impact type piezoelectric actuator in a first direction,the second circuit and the fourth circuit are alternately switched on.In a time period from t1 to t2, the control signals I and V are switchedon, so that the switching circuits 621 and 625 constituting the secondcircuit are switched on. Thus, a predetermined short circuited currentflows from the electric power supply 63 to the ground through thepiezoelectric device 31 a or 31 b. The electric charge is charged intothe piezoelectric device 31 a or 31 b in a direction from the electrodeP+ to the electrode P− due to the capacitance thereof. Thus, the voltagebetween the electrodes P+ and P− rapidly increases to a level of thevoltage VP of the electric power supply 63. The level of the voltage VPis set to be lower than the level of the inversion of the polarizationof the ceramic thin plate of the piezoelectric device 31 a or 31 b. Inthis time period, the slider 33 a shown in FIGS. 8 and 9 is not movedwith respect to the stationary member 30 a. Similarly, the driving unit30 b shown in FIGS. 10 and 11 is not moved with respect to the basemember 34 b.

In a time period from t3 to t4, the control signals II and III areswitched on, so that the switching circuit 622 and the constant currentcircuit 623 constituting the fourth circuit are switched on. In thefourth circuit, a predetermined constant current flows into thepiezoelectric device 31 a or 31 b in a direction from the electrode P−to the electrode P+, so that the electric charge charged at the time t2gradually reduces. In other words, the electric charge charged in thepiezoelectric device 31 a or 31 b is gradually discharged. Thus, thevoltage between the electrodes P+ and P− gradually decreases to a levelof the voltage −VP. In this time period, the slider 33 a shown in FIGS.8 and 9 is moved in the first direction with respect to the stationarymember 30 a. Similarly, the driving unit 30 b shown in FIGS. 10 and 11is relatively moved in the first direction with respect to the basemember 34 b.

For driving the impact type piezoelectric actuator in a second directionopposite to the first direction, the rising up of the driving signal Dis gradually increased and the falling down thereof is rapidlyincreased. Concretely, output timings of the control signals from thecontrol circuit 51 is adjusted in a manner so that the control signalsII and IV are switched on in a time period from t11 to t12 for switchingon the third circuit, and the control signals I and VI are switched onin a time period from t13 to t14 for switching on the first circuit.

Seventh Embodiment

A driving apparatus in a seventh embodiment of the present invention isdescribed with reference to FIGS. 22 and 23. The driving apparatus ofthe seventh embodiment is suitable for driving the impact typepiezoelectric actuators in the third embodiment shown in FIGS. 8 to 11.The block diagram of the driving apparatus in the seventh embodiment issimilar to that in the fifth embodiment shown in FIG. 17, so that theillustration thereof is omitted. The bipolar transistors in FIGS. 18Cand 18D in the fifth embodiment are replaced by MOSFET in the seventhembodiment.

A circuit diagram of the driving apparatus in the seventh embodiment isshown in FIG. 22. As can be seen from FIG. 22, four circuits areprovided between an electric power supply 73 and the ground, in whichthe circuits are connected to the piezoelectric device 31 a or 31 b forconfiguring a series circuit. Symbols P+ and P− added to thepiezoelectric device 31 a or 31 b show the electrodes standardized bythe polarization of the ceramic thin plate of the piezoelectric device.

A first circuit is configured by a constant current circuit 721 forsupplying a predetermined limited current to the piezoelectric device 31a or 31 b and a switching circuit 726. The first circuit serves as adischarge circuit for gradually discharging the electric charge from thepiezoelectric device 31 a or 31 b in a direction from the electrode P+to the electrode P−.

A second circuit is configured by switching circuits 722 and 726. Thesecond circuit serves as a quick charge circuit for quickly charging theelectric charge from the electric power supply 73 into the piezoelectricdevice 31 a or 31 b in a direction from the electrode P+ to theelectrode P−.

A third circuit is configured by switching circuits 723 and 725. Thethird circuit serves as a quick charge circuit for quickly charging theelectric charge from the electric power supply 73 into the piezoelectricdevice 31 a or 31 b in a direction from the electrode P− to theelectrode P+.

A fourth circuit is configured by a constant current circuit 724 forsupplying a predetermined limited current to the piezoelectric device 31a or 31 b and the switching circuit 725. The fourth circuit serves as adischarge circuit for gradually discharging the electric charge from thepiezoelectric device 31 a or 31 b in a direction from the electrode P−to the electrode P+.

The switching circuits 722, 723, 725 and 726 are respectively configuredby a MOSFET which includes a parasitic diode connected in parallelthereto illustrated by dotted line in the figure.

In FIG. 23, the driving signal D shows a waveform standardized by thepolarization direction of the ceramic thin plate of the piezoelectricdevice. The control signals I to VI respectively correspond to timingsignals for switching on and off of the above-mentioned circuits 721 to726. The painted regions of the control signals I to VI by blackrespectively show the timings in which the control signals are switchedon for switching on the circuits 721 to 726.

An operation of the impact type piezoelectric actuator by the drivingapparatus in the seventh embodiment is described with reference to FIG.23.

For driving the impact type piezoelectric actuator in a first direction,the first circuit and the third circuit are alternately switched on. Ina time period from t1 to t2, the control signals II and VI are switchedon, so that the switching circuits 722 and 726 constituting the secondcircuit are switched on. Thus, a predetermined short circuited currentflows from the electric power supply 73 to the ground through thepiezoelectric device 31 a or 31 b. The electric charge is charged intothe piezoelectric device 31 a or 31 b in a direction from the electrodeP+ to the electrode P− due to the capacitance thereof. Thus, the voltagebetween the electrodes P+ and P− rapidly increases to a level of thevoltage VP of the electric power supply 73. The level of the voltage VPis set to be lower than the level of the inversion of the polarizationof the ceramic thin plate of the piezoelectric device 31 a or 31 b. Inthis time period, the slider 33 a shown in FIGS. 8 and 9 is not movedwith respect to the stationary member 30 a. Similarly, the driving unit30 b shown in FIGS. 10 and 11 is not moved with respect to the basemember 34 b.

In a time period from t3 to t4, the control signals IV and V areswitched on, so that the constant current circuit 724 and the switchingcircuit 725 constituting the fourth circuit are switched on. In thefourth circuit, a predetermined constant current flows into thepiezoelectric device 31 a or 31 b in a direction from the electrode P−to the electrode P+, so that the electric charge charged at the time t2gradually reduces. In other words, the electric charge charged in thepiezoelectric device 31 a or 31 b is gradually discharged. Thus, thevoltage between the electrodes P+ and P− gradually decreases to a levelof the voltage −VP.

When the electrode P+of the piezoelectric device 31 a or 31 b is shortcircuited by switching on of the switching circuit 725 at the time t3,the electric charge in the piezoelectric device 31 a or 31 b flowsthrough the parasitic diode of the switching circuit 726 which is at offstate. Thus, the potential of the electrode P− of the piezoelectricdevice 31 a or 31 b rapidly falls down to 0V as shown by solid line inthe time period from t3 to t3-1 on the waveform of the driving signal Din FIG. 23. After the parasitic diode cannot serve, the electric chargein the piezoelectric device 31 a or 31 b is gradually discharged along aincline similar to the incline illustrated by dotted line in FIG. 23.

In the seventh embodiment, parts of the driving circuit are configuredby the MOSFETs, so that switching speed of the transistors can be madefaster, and the consumption of the electric current by the drivingcircuit can be reduced. The electric charge in the piezoelectric device31 a or 31 b is rapidly discharged by the parasitic diode until thepotential of both electrodes P+ and P− becomes 0V, so that there is apossibility to deteriorate the output characteristics of the impact typepiezoelectric actuator. However, it was actually no problem in theoutput characteristics of the impact type piezoelectric actuator when itwas driven by the driving signal having the waveform shown in FIG. 23.

In this time period from t3 to t4, the slider 33 a shown in FIGS. 8 and9 is moved in the first direction with respect to the stationary member30 a. Similarly, the driving unit 30 b shown in FIGS. 10 and 11 isrelatively moved in the first direction with respect to the base member34 b.

For driving the impact type piezoelectric actuator in a second directionopposite to the first direction, the rising up of the driving signal Dis gradually increased and the falling down thereof is rapidlyincreased. Concretely, output timings of the control signals from thecontrol circuit 71 is adjusted in a manner so that the control signals Iand VI are switched on in a time period from t11 to t12 for switching onthe third circuit, and the control signals III and V are switched on ina time period from t13 to t14 for switching on the first circuit.

Eighth Embodiment

A driving apparatus in an eighth embodiment of the present invention isdescribed with reference to FIGS. 24 and 25. The driving apparatus ofthe eighth embodiment is suitable for driving the impact typepiezoelectric actuators in the third embodiment shown in FIGS. 8 to 11.The block diagram of the driving apparatus in the eighth embodiment issimilar to that in the fifth embodiment shown in FIG. 17, so that theillustration thereof is omitted. The bipolar transistors in FIGS. 20Cand 20D in the sixth embodiment are replaced by MOSFET in the eighthembodiment.

A circuit diagram of the driving apparatus in the eighth embodiment isshown in FIG. 24. As can be seen from FIG. 24, four circuits areprovided between an electric power supply 83 and the ground, in whichthe circuits are connected to the piezoelectric device 31 a or 31 b forconfiguring a series circuit. Symbols P+ and P− added to thepiezoelectric device 31 a or 31 b show the electrodes standardized bythe polarization of the ceramic thin plate of the piezoelectric device.

A first circuit is configured by a switching circuit 821 and a constantcurrent circuit 826 for supplying a predetermined limited current to thepiezoelectric device 31 a or 31 b. The first circuit serves as adischarge circuit for gradually discharging the electric charge from thepiezoelectric device 31 a or 31 b in a direction from the electrode P+to the electrode P−.

A second circuit is configured by switching circuits 821 and 825. Thesecond circuit serves as a quick charge circuit for quickly charging theelectric charge from the electric power supply 83 into the piezoelectricdevice 31 a or 31 b in a direction from the electrode P+ to theelectrode P−.

A third circuit is configured by switching circuits 822 and 824. Thethird circuit serves as a quick charge circuit for quickly charging theelectric charge from the electric power supply 83 into the piezoelectricdevice 31 a or 31 b in a direction from the electrode P− to theelectrode P+.

A fourth circuit is configured by the switching circuit 822 and aconstant current circuit 823 for supplying a predetermined limitedcurrent to the piezoelectric device 31 a or 31 b. The fourth circuitserves as a discharge circuit for gradually discharging the electriccharge from the piezoelectric device 31 a or 31 b in a direction fromthe electrode P− to the electrode P+.

The switching circuits 821, 822, 824 and 825 are respectively configuredby a MOSFET which includes a parasitic diode connected in parallelthereto illustrated by dotted line in the figure.

In FIG. 25, the driving signal D shows a waveform standardized by thepolarization direction of the ceramic thin plate of the piezoelectricdevice. The control signals I to VI respectively corresponds to timingsignals for switching on and off of the above-mentioned circuits 821 to826. The painted regions of the control signals I to VI by blackrespectively show the timings in which the control signals are switchedon for switching on the circuits 821 to 826.

An operation of the impact type piezoelectric actuator by the drivingapparatus in the eighth embodiment is described with reference to FIG.25.

For driving the impact type piezoelectric actuator in a first direction,the first circuit and the third circuit are alternately switched on. Ina time period from t1 to t2, the control signals I and V are switchedon, so that the switching circuits 821 and 825 constituting the secondcircuit are switched on. Thus, a predetermined short circuited currentflows from the electric power supply 83 to the ground through thepiezoelectric device 31 a or 31 b. The electric charge is charged intothe piezoelectric device 31 a or 31 b in a direction from the electrodeP+ to the electrode P− due to the capacitance thereof. Thus, the voltagebetween the electrodes P+ and P− rapidly increases to a level of thevoltage VP of the electric power supply 83. The level of the voltage VPis set to be lower than the level of the inversion of the polarizationof the ceramic thin plate of the piezoelectric device 31 a or 31 b. Inthis time period, the slider 33 a shown in FIGS. 8 and 9 is not movedwith respect to the stationary member 30 a. Similarly, the driving unit30 b shown in FIGS. 10 and 11 is not moved with respect to the basemember 34 b.

In a time period from t3 to t4, the control signals II and III areswitched on, so that the switching circuit 822 and the constant currentcircuit 823 constituting the fourth circuit are switched on. In thefourth circuit, a predetermined constant current flows into thepiezoelectric device 31 a or 31 b in a direction from the electrode P−to the electrode P+, so that the electric charge charged at the time t2gradually reduces. In other words, the electric charge charged in thepiezoelectric device 31 a or 31 b is gradually discharged. Thus, thevoltage between the electrodes P+ and P− gradually decreases to a levelof the voltage −VP.

When the electrode P+ of the piezoelectric device 31 a or 31 b is shortcircuited by switching on of the switching circuit 824 at the time t3,the electric charge in the piezoelectric device 31 a or 31 b flowsthrough the parasitic diode of the switching circuit 825 which is at offstate. Thus, the potential of the electrode P− of the piezoelectricdevice 31 a or 31 b rapidly falls down to 0V as shown by solid line inthe time period from t3 to t3-1 on the waveform of the driving signal Din FIG. 25. After the parasitic diode cannot serve, the electric chargein the piezoelectric device 31 a or 31 b is gradually discharged along aincline similar to the incline illustrated by dotted line in FIG. 25.

In the eighth embodiment, parts of the driving circuit are configured bythe MOSFETs, so that switching speed of the transistors can be madefaster, and the consumption of the electric current by the drivingcircuit can be reduced. The electric charge in the piezoelectric device31 a or 31 b is rapidly discharged by the parasitic diode until thepotential of both electrodes P+ and P− becomes 0V, so that there is apossibility to deteriorate the output characteristics of the impact typepiezoelectric actuator. However, it was actually no problem in theoutput characteristics of the impact type piezoelectric actuator when itwas driven by the driving signal having the waveform shown in FIG. 23.

In this time period from t3 to t4, the slider 33 a shown in FIGS. 8 and9 is moved in the first direction with respect to the stationary member30 a. Similarly, the driving unit 30 b shown in FIGS. 10 and 11 isrelatively moved in the first direction with respect to the base member34 b.

For driving the impact type piezoelectric actuator in a second directionopposite to the first direction, the rising up of the driving signal Dis gradually increased and the falling down thereof is rapidlyincreased. Concretely, output timings of the control signals from thecontrol circuit 81 is adjusted in a manner so that the control signalsII and IV are switched on in a time period from t11 to t12 for switchingon the third circuit, and the control signals I and VI are switched onin a time period from t13 to t14 for switching on the first circuit.

Ninth Embodiment

A driving apparatus in a ninth embodiment of the present invention isdescribed with reference to FIG. 26. The driving apparatus of the ninthembodiment is suitable for driving the impact type piezoelectricactuators in the third embodiment shown in FIGS. 8 to 11. The blockdiagram of the driving apparatus in the ninth embodiment is similar tothat in the fifth embodiment shown in FIG. 17, so that the illustrationthereof is omitted.

FIG. 26 shows a main part of a circuit diagram of the driving apparatusin the ninth embodiment, in which switching circuits 925 and 926configured by MOSFETs replace the switching circuits 725 and 726configured by the bipolar transistors in FIG. 22 showing the circuitdiagram of the driving circuit in the seventh embodiment. Furthermore,diodes 925 a and 926 a are connected as series connection to the MOSFETsof the switching circuits 925 and 926 in forward direction (oppositedirection to the parasitic diodes shown by dotted lines).

The diodes 925 a and 926 a are effective for easing the rapid dischargeof the electric charge from the piezoelectric device 31 a or 31 b by theparasitic diodes of the MOSFETs, if the deterioration of the outputcharacteristics of the impact type piezoelectric actuator due to therapid falling down of the potential of the piezoelectric device 31 a or31 b becomes problem.

Tenth Embodiment

A driving apparatus in a tenth embodiment of the present invention isdescribed with reference to FIG. 27. The driving apparatus of the tenthembodiment is suitable for driving the impact type piezoelectricactuators in the third embodiment shown in FIGS. 8 to 11. The blockdiagram of the driving apparatus in the tenth embodiment is similar tothat in the fifth embodiment shown in FIG. 17, so that the illustrationthereof is omitted.

FIG. 27 shows a main part of a circuit diagram of the driving apparatusin the tenth embodiment, in which switching circuits 1021 and 1022configured by MOSFETs replace the switching circuits 821 and 822configured by the bipolar transistors in FIG. 24 showing the circuitdiagram of the driving circuit in the eighth embodiment. Furthermore,diodes 1021 a and 1022 a are connected as series connection to theMOSFETs of the switching circuits 1021 and 1022 in forward direction(opposite direction to the parasitic diodes shown by dotted lines).

The diodes 1021 a and 1022 a are effective for easing the rapiddischarge of the electric charge from the piezoelectric device 31 a or31 b by the parasitic diodes of the MOSFETs, if the deterioration of theoutput characteristics of the impact type piezoelectric actuator due tothe rapid falling down of the potential of the piezoelectric device 31 aor 31 b becomes problem.

Although the present invention has been fully described by way ofexample with reference to the accompanying drawings, it is to beunderstood that various changes and modifications will be apparent tothose skilled in the art. Therefore, unless otherwise such changes andmodifications depart from the scope of the present invention, theyshould be construed as being included therein.

1. A driving apparatus for driving a piezoelectric device serving as adriving source of an actuator comprising: a first circuit for graduallydischarging electric charge from the piezoelectric device in a firstdirection; and a second circuit for quickly charging electric chargeinto the piezoelectric device in a second direction opposite to thefirst direction; a third circuit for gradually discharging electriccharge from the piezoelectric device in the second direction; a fourthcircuit for quickly charging electric charge into the piezoelectricdevice in the first direction; and a controller for controllingalternative of a group of the first and second circuits and anothergroup of the third and fourth circuits corresponding to a drivingdirection of the actuator.
 2. The driving apparatus in accordance withclaim 1, wherein the first circuit includes a first switching circuitconnected to a first current circuit for supplying a first current tothe piezoelectric device; the second circuit includes a second switchingcircuit connected to a second current circuit for supplying a secondcurrent which is larger than the first current to the piezoelectricdevice; the third circuit includes a third switching circuit connectedto a third current circuit for supplying a third current substantiallythe same intensity as the first current to the piezoelectric device; thefourth circuit includes a fourth switching circuit connected to a fourthcurrent circuit for supplying a fourth current which is substantiallythe same intensity as the second current to the piezoelectric device;and the controller alternatively switching on and off the firstswitching circuit and the second switching circuit of the thirdswitching circuit and the fourth switching circuit.